The need to convey a product is frequently encountered during many industrial processes. For example, an extruder is a well known apparatus utilized to provide continuous mixing and conveyance of ingredients of a product. Extruders are widely used in many industries, e.g. the chemical and food processing industries, to continuously mix ingredients of a product and to form the product by conveying the mixed ingredients through a die having a preselected shape. The continuous processing provided by an extruder often results in an efficient and cost effective alternative to batch processing techniques.
Extruders typically include an arrangement of inlet ports for ingress of various ingredients to be mixed by the extruder, into a mixing chamber. The mixed ingredients are forced through the extrusion die of the extruder by the conveying action of various mechanical elements and onto a conveyor or other processing mechanism for cutting and further processing. The cross-section of the extrusion die is arranged to form the mixed ingredients (referred to as the extrudate), as it is forced through the egress end of the extrusion die, into a desired shape for the product.
Conveyance of a mixture of ingredients through a die often occurs under laminar flow conditions. Product flow under these conditions causes maximum flow velocity at the center of flow, with those portions of the product in contact with surfaces, such as, e.g., extrusion die surfaces, tending to adhere to the surfaces due to the friction. In such circumstances, it is typical for the surfaces of the mixed ingredients in contact with the surfaces of the extrusion die to encounter friction due to the relative movement of the product over the extruder surfaces. This results in shear forces throughout the product as it is conveyed through the extruder and forced through the extrusion die.
The presence of laminar flow with shear forces can degrade product quality. This is particularly true in shear sensitive products, i.e., products that are susceptible to degradation due to the shear forces. Thus, the advantages of continuous mixing and conveying afforded by extrusion processing can be lost due to product degradation when a shear sensitive product is extruded, particularly when the shear sensitive product is of a relatively high viscosity. Moreover, the shear forces can cause physical break up of the product as it is forced through an extrusion die, resulting in degradation of the internal structure and loss of integrity of the product.
In certain ingredient-mixing operations, desired chemical reactions occur between the ingredients. Often the chemical reactions affect the rheological properties of the product. For example, a setting solution can be mixed with other liquid ingredients to set the ingredients into a solid or gel state for shaping and forming. Setting reactions are also utilized to reconstitute food products so that solutions, e.g., containing a source ingredient, can be reconstituted into a gel having the texture and consistency of the original food product used to provide the source ingredient.
A problem with utilizing a continuous extrusion process to obtain a set extrudate having a preselected shape is that when the product begins to set within the extruder, the possibility of degradation and physical break up of the extrudate during conveyance increases after the transition of the mixed ingredients from a liquid phase to a highly viscous solid or gel phase. The high viscosity of the setting gel increases shear forces throughout the gel or gelled product as it is conveyed through the extruder. When the final mixture of the product is shear sensitive, the extrudate tends to degrade and break apart, at least sporadically, as it is conveyed through the extrusion die, significantly limiting the ability to continuously convey, shape, form and cut the extrudate so as to produce an extrudate having a preselected shape in an efficient and continuous manner.
Thus, the desirability and efficiency of continuously processing and conveying ingredients undergoing a simultaneous chemical setting reaction becomes problematical, particularly in an extrusion process involving mixtures that produce gelled products. The inherent continuous mixing, conveying, forming and shaping aspects of an extrusion operation are rendered ineffective for shear sensitive products, especially those undergoing setting reactions that produce gelled products, due to a continuously increasing viscosity and resultant generation of damaging shear forces, as the mixed ingredients undergo transition from a liquid phase to a gel during conveyance through the extruder. Until recently, systems were not known that could provide a method of product conveyance suitable to reduce shear forces so that, for example, an extrusion process of the type described above can be effectively performed to produce gelled extrudates having a preselected shape.
A method and apparatus for overcoming these problems are disclosed in a co-pending application, U.S. Ser. No. 08/023,997, filed Feb. 26, 1993, which is herein incorporated in its entirety by reference, and continuing applications therefrom, which are directed to a two phase conveyance method for transporting shear sensitive extrusion products. While such a method has been found to be useful for reducing or eliminating physical break up and loss of integrity of shear sensitive extrusion products having a preselected shape, improvements in reliability and consistency in performance are disclosed herein when this method is used for high-volume, mass production processes for producing food products that are typically subjected to wide variations in the process conditions and in raw material properties.
It is known that food products, for example, onion rings, may be produced using a process for preparing a shaped and extruded food product wherein a slurry of a food product and an ungelled gel-forming material that normally forms a gel upon exposure to a gelation agent is extruded into an elemental shape while washing the surface thereof with a gelation agent, U.S. Pat. No. 3,650,765. The gelation agent causes immediate formation of a gel skin onto the extruded shape, the skin thus enveloping slurry during further extrusion. The final extrusion product is subjected to further processing to stabilize the slurry. Based on this method, an improved method for forming and discharging the food product has been disclosed, U.S. Pat. No. 4,702,687.
Onion rings currently on the market are typically made from either fresh, natural onions or formed from dried, diced onions using a mass production method such as disclosed in U.S. Pat. No. 4,702,687. The natural product has quality advantages over the formed product. However, the formed onion rings are more suitable for quick service restaurants, which need portion control and consistent cost per serving.
Natural onion rings are made from white onions or yellow onions. The natural onions that are typically used to make onion rings are referred to as "ringers". Ringer onions typically yield more usable rings and have a relatively small amount of double hearts. Onions are seasonal and the quality depends on the variety, season, soil type, climatic conditions and growing practices. As a result, natural onions perform inconsistently during processing. In addition, natural onions spoil during storage such that storage onions may cause processing problems.
Natural onions are typically topped, tailed, peeled and sliced and the individual rings are separated from each other prior to processing. There is a significant loss during this preparatory step. The losses can amount to 30-40% by weight of the onions. Also, the ring thickness varies from ring to ring and results in non-uniform product. Additionally, there is a large variation in the size, shape, weight, flavor and texture of rings made from natural onions.
Battered and breaded natural onion rings are served as an appetizer or side dish in restaurants. Higher-quality, higher-priced restaurants typically serve natural onion rings made on-site and cooked to order. However, natural onions do not hold up well under heat lamps. Higher priced restaurants, thus, must maintain the quality of onion rings served to their customers by constantly obtaining a fresh supply of onions for which they are able to charge a premium price. On the other hand, lower-priced restaurants, as well as value-priced quick service restaurants, serve onion rings fried back from a frozen condition. These restaurants typically sell onion rings as an appetizer or a side dish and charge much less.
Few quick service restaurants have onion rings on their menu. One of the hurdles is that it is very hard to maintain the quality and consistency of the natural product. Also, the cost per serving of natural onion rings places them at a price point higher than what a typical fast-food consumer may be willing to pay. Some fast food restauranteurs have mass-produced formed onion rings on their menu. These formed onion rings are made from dried, diced onions and are perceived to have a lower quality than battered and breaded natural onion rings. In particular, these formed onion rings have a substantially different, generally less desirable taste, texture, flavor and visual appearance, as compared to natural onion rings.
Natural onion products are susceptible to freeze-thaw cycles. Onions are composed mostly of water (&gt;80%) and contain carbohydrates, including pectic substances and fibers and minerals. When frozen and thawed, natural onions typically lose their cellular integrity.
For natural onion rings, separation of the onions from the batter and breading coating system may occur because of excessive shrinkage of the onion rings during cooking. As a result, when someone bites into a battered and breaded natural onion ring, the onion ring may pull out of the coating system and fall on the person's chin causing what is referred to as "chin burn". Because of this problem, natural onion rings are not considered suitable as convenience food products or as hand-held products, which can be eaten by consumers while engaged in another activity such as walking, driving, etc.